The invention relates specifically to laser angioplasty and to improved methods and apparatus therefor. With this in mind, the invention will be specifically described with reference to laser systems and methods for ablating plaque, although it has broader applicability. For example, it is applicable to the so called hot probe laser approach as described in U.S. Pat. No. 4,650,024, entitled "Thermorecanalization Catheter and Method for Use", issued March 31, 1987. In its broader sense the invention relates to any medical treatment systems and method for effecting treatment to selected sites in the body in which cyclic or repetitive movement is involved.
The aiming of laser energy accurately at atherosclerotic plaque within a vessel, such as a coronary artery, is negatively affected by the continuous movement of the vessel. This movement is associated with cardiac contractions, hence relates to phases of the cardiac cycle. As a result of such movement a laser catheter positioned within a vessel also undergoes relative movement and may at times be aimed at plaque and at other times aimed at normal vessel wall.
Mechanical damage to vessels, including wall perforation, continues to be a major problem with laser angioplasty. The aiming of laser energy (delivered via a fiberoptic delivery system) is a major task. The continuous motion of the vessel wall significantly complicates aiming and delivering of laser energy accurately to the atherosclerotic plaque. The prior art has treated the movement of coronary arteries and other vessels as a problem rather than attempting to take advantage of the repetitive nature of the movement of coronary arteries as displayed from one cardiac cycle to another.
The present invention relates to a control system for timing the delivery of laser energy such that it accurately impinges on plaque or other intended target area.